Washington Park, Illinois has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 8.4 °C (low) to 19.2 °C (high). Annual precipitation averages 1149.4 Millimeters. Washington Park is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -4.7 °C | 4.6 °C | 69.09 mm |
| February | -2.8 °C | 7.5 °C | 61.21 mm |
| March | 2 °C | 13.1 °C | 89.92 mm |
| April | 8.1 °C | 19.8 °C | 122.68 mm |
| May | 13.9 °C | 24.8 °C | 133.86 mm |
| June | 18.9 °C | 29.8 °C | 126.49 mm |
| July | 20.9 °C | 31.7 °C | 113.28 mm |
| August | 19.9 °C | 30.9 °C | 98.81 mm |
| September | 15.1 °C | 27.3 °C | 86.36 mm |
| October | 8.7 °C | 20.9 °C | 83.06 mm |
| November | 2.7 °C | 13.2 °C | 93.22 mm |
| December | -2.3 °C | 6.9 °C | 71.37 mm |
| Annual | 8.4 °C | 19.2 °C | 1149.35 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |